7 A particle \(P\) is projected from a point \(O\) on a horizontal plane and moves freely under gravity. The initial velocity of \(P\) is \(100 \mathrm {~ms} ^ { - 1 }\) at an angle \(\theta\) above the horizontal, where \(\tan \theta = \frac { 4 } { 3 }\). The two times at which \(P\) 's height above the plane is \(H \mathrm {~m}\) differ by 10 s .

1. Find the value of \(H\).
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2. Find the magnitude and direction of the velocity of \(P\) one second before it strikes the plane.
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